Cub engine rolls up and down

Nicholas Whitman · Dec 10, 2009

I am plowing and pushing brush with a 1956 Cub. I have a recurring problem with the engine speed "rolling" up and down.

This condition is sometimes brought on by the plow hitting a stationary object - stump stub for example - when the tractor comes to an abrupt stop. It gets bounced around pretty good when pushing snow. There is plenty of moisture when plowing but not pushing brush. Tractor resides in a heated garage in winter. Spark is ok. 12 volt conversion lets her start right up.

My best guess is it is caused by dirt getting into the carburetor which is shaken loose. If I remove and blow out the carb I am back in business. Though I never find a smoking gun. I do catch rust/dirt in the bowl, but I clean out the bowl and screen as well as the screen at the start of the carb. My tank interior isn't perfect but I'd rather not have to do a full treatment on it. My fuel comes in clean. I'm not working in a dusty environment. My thought is the screens just aren't preventing dirt from getting through. What would you guys think of adding an line fuel filter?

Many thanks for your thoughts.

ScottyHOMeY · Dec 10, 2009

A couple of thoughts.

Is the engine speed going up and down, or are you just hearing a change in motor sound as the governor supplies more fuel under load? If the latter, that's all quite normal. (Exhaust sound does not necessarily equate to engine speed.) If it actually speeds up or slows down under a STEADY load, there is a screw on the front of the governor that adjusts the bumper spring to smooth it out. That probably is not necessary if the only changes you hear are when the load changes.

Your question about the fuel filter will generate some comments both in favor and against. It sounds as if you tend your fuel system well, and I really doubt that fuel supply is contributing to what may or may not be a problem. If you do want to try a filter, talk to a good counterman at your auto supply. It's important that you have one that's made for a gravity feed system. Putting one made for a pump-supplied fuel system on your tractor will only create a restriction in the line and make for a whole other set of undesirable symptoms.

old · Dec 10, 2009

Most of the time that is caused by a carb running lean and may need to be adjusted if it has an adjustable main jet or cleaned if it does not. NO DO NOT put on an in line fuel filter because that will just make your lack of fuel problem worse

Nicholas Whitman · Dec 10, 2009

Engine "rolls" at idle and revved. It looses quite a bit of power when it is doing this - though I can usually limp home. Governor is activly moving the throtle linkage - maby it is compensating for the carb - or maby it is the problem.

This governor does work - but not as smoothy as it should. I know this becaue on my other cub -a 1960s model - the governor is really smooth and responsive. I'm not a skiller mechanic so I had my shop look at it. It was cleaned but never brought up to snuff.

gene bender · Dec 10, 2009

If you do install an inline filter get the ones from Fram you can see thru them and they will catch fines the screen in the sediment bowl wont. Easy to change just point them in the rite direction and they work fine i have used them for many yrs but they will plug as like i said they catch dirt the screen doesent.

ScottyHOMeY · Dec 10, 2009

In that case, I'd make sure the carb itself is good and clean and the float and needle in good shape and adjusted, and then make sure, as old suggested, that you aren't just set too lean. From there, if that doesn't get it, I'd start looking at the governor. If the problem strikes you as radical, or if it can't be adjusted out with the bumper spring screw, then it's probably time to open it up and have a look at the main spring and everything else.

Nicholas Whitman · Dec 10, 2009

Pulled the carb drain plug - good flow there. Cleaned the bowl and inline screens. Found some small particles of red paint/rust, but not enough to impead flow. Dissassembled carb - no dirt evident. Float and valves are good - replaced a couple of years ago. Blew carb cleaner through passages and reassembled. Set the mixture screw at two turns out - usually set to 1.5 - so a bit richer as suggested.

I have never adjusted the governor. Took a look and found the bumper spring screw was socked down all the way - no thread showing. Removed the whole threaded assembly. It look good, spring and ball on end seemed ok. Reinstalled with about 1/4 inch thread showing.

Tractor started right up. Gave her a run pushing back the snow banks. Ran without "rolling" once.

Can't exactly say what fixed it but we're operational.

Thanks for all your assistance!

Nicholas Whitman · Dec 10, 2009

Pulled the carb drain plug - good flow there. Cleaned the bowl and inline screens. Found some small particles of red paint/rust, but not enough to impead flow. Dissassembled carb - no dirt evident. Float and valves are good - replaced a couple of years ago. Blew carb cleaner through passages and reassembled. Set the mixture screw at two turns out - usually set to 1.5 - so a bit richer as suggested.
I have never adjusted the governor. Took a look and found the bumper spring screw was socked down all the way - no thread showing. Removed the whole threaded assembly. It look good, spring and ball on end seemed ok. Reinstalled with about 1/4 inch thread showing.

Tractor started right up. Gave her a run pushing back the snow banks. Ran without "rolling" once.

Can't exactly say what fixed it but we're operational.

Thanks for all your assistance!

Dellbertt · Dec 10, 2009

I had an H that did the same thing. I drained the tank, blew it out with air, added a gravity feed inline filter and it ran fine for years.
Don't let anyone tell you not to add an inline filter.
Make up your own mind.
Dell

ScottyHOMeY · Dec 10, 2009

Good news! and thanks for reporting back.

That's always the danger of fixing a couple fo things at once, you're never sure which one did the job. So old and I I can go have a fight about which one of us was right!

Not.

Glad she's goin' right. If I was a help, you're certainly welcome. That's what we try to do here.

Dave H (MI) · Dec 10, 2009

"So old and I I can go have a fight about which one of us was right!

Not."

C'mon! It's been a whole couple days since we had a good pi$$ing contest on here! Besides, I'm thinking you could take him. I got your back.

ScottyHOMeY · Dec 10, 2009

john *.?-!.* cub owner · Dec 11, 2009

Nicholas, look closely at where the cross shaft (rod going across front of engine and into governor) goes into the fitting on the governor. It is common for it to develop play there from wear on the shaft and woodruff key. Only very slight play can cause a lot of surging, delayed response, etc. easy solution is to remove the rod and put some loctite on it and reinstall, unless it is so loose it needs a bushing. coke can is good for making bushing out of.

Nicholas Whitman · Dec 14, 2009

Well boys let's not give up the hope of a fight!

Went to push some ice off the road as it is 40 degrees. Had a flawless 100 yard run and then the rolling came back! Richened up the mixture to two turns out from one and a half - no difference. Brought it in to one turn out - no difference. There is dampness in the air and some icing was showing on the carburetor. Tractor lives indoors and no water is showing in the bowl. Governor was active and seemed to be trying to compensate for the uneven running. Thoughts?

Cub engine rolls up and down

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